The present invention relates to a television receiver that receives moving picture data and displays it, and in particular, to a television receiver that has a decoding circuit that receives encoded digital moving picture data and decodes the data and a picture processing method thereof.
In recent years, as digital television broadcasts, DVDs (Digital Versatile Disks), and so forth have been outspread, high quality picture data and sound data have become common. As such mediums have been outspread, television receivers that receive high quality picture data and sound data and output them to a television monitor and a speaker have been developed. Picture data and sound data of digital television broadcasts and DVDs are provided in a data format in which data has been encoded according to a digital moving picture encoding system, such as MPEG-2 (Moving Picture Experts Group-2).
In MEPG-2, when data is encoded, a picture of, for example, an object that moves in fields (or frames) is detected. The difference between a field in which the motion is predicted and the current field is extracted. As a result, the difference is output as a P picture and a B picture. In addition, the motion is output as motion information (moving vector information). MPEG-2 encoded data are decoded with a P picture and a B picture, which are difference data, and the motion information. With the difference data and the motion information, the size of encoded data can be more compacted without deterioration of the picture quality of decoded data.
In the conventional television receiver, a video signal in which MPEG-2 encoded data and so forth have been decoded is supplied as an input signal. Since this type of television receiver directly inputs a video signal, the receiver does not need to have a circuit that decodes MPEG-2 encoded data. Thus, the television receiver can be accomplished with simple circuitry. When the television receiver performs a compensation process and a noise reduction (NR) process corresponding to the motion of a picture, the television receiver needs to detect a motion in field (frame) pictures with the received video signal and obtain motion information once again.
A picture signal processing apparatus that receives a video signal, detects motion information from the video signal, and selectively performs a frame NR process or a field NR process according to the detected result of the motion information has been proposed in Japanese Patent Laid-Open Publication No. 2002-51234.
However, since the conventional television receiver receives a video signal in the foregoing manner, the television receiver needs to perform the motion detection process for each picture of the video signal to obtain motion information of pictures. Thus, when picture data are encoded according to MPEG-2, although motion information is generated, the conventional television receiver cannot use the motion information. The real noise reduction process or the like detects motion information from an input video signal and determines whether an objective field (frame) is a moving picture or a still picture according to the motion information. Thus, the determination accuracy of the noise reduction process is restricted.
In addition, since the television receiver needs to have a circuit that detects a motion, the circuit scale becomes large.
Moreover, it is very difficult to determine whether an entire pattern is a moving picture or a still picture. Thus, depending on a moving pattern, the determination circuit may malfunction. As a result, the reproduction quality of the moving picture deteriorates.
For example, in a noise reduction process circuit that determines whether an object frame is a moving picture or a still picture and adds information of successive frames at a predetermined ratio when the object frame is a still picture, when pictures that slightly move are input to the circuit, since the amount of motion of the input pictures is small, if a moving/still picture determination circuit determines that the input pictures are still pictures, phenomena take place in which, for example, the contour of the picture becomes dim or the picture has a tail.
To suppress the occurrence of such phenomena, if a threshold value by which an object frame is determined to be a moving picture or a still picture is offset to the moving picture side, many pictures are determined to be a moving picture. Thus, the noise reduction process cannot be sufficiently performed.
FIG. 6 shows an example in which the conventional moving/still picture determination circuit malfunctions. FIG. 6A conceptually shows an input stream. In FIG. 6A, a center object denoted by hatched lines slightly moves in arrow directions. Although this stream needs to be determined to be a moving picture, since the amount of motion is small, it is assumed that the stream has been determined to be a still picture.
FIG. 6B conceptually shows the state in which, since an input stream has been determined to be a still picture, in the noise reduction process, several successive frames are added at a predetermined ratio. FIG. 6C shows a picture in which several successive frames have been added at a predetermined ratio. Since an object displayed in each frame actually slightly moves, when these frames are added, as shown in FIG. 6C, the contour of the input stream becomes dim and the picture of the object is displayed as if the object had a tail.
Therefore, an object of the present invention is to provide a television receiver and a picture processing method that determine whether an input stream is a moving picture or a still picture with motion information obtained from encoded data according to a digital moving picture encoding system such as MPEG-2 and perform a different picture process corresponding to the determined result.
Another object of the present invention is to provide a television receiver and a picture processing method that capture motion information from encoded data according to the digital moving picture encoding system such as MPEG-2 without the need to have a motion detection circuit.
A further object of the present invention is to provide a television receiver and a picture processing method that select a mode in which encoded data according to the digital moving picture encoding system such as MPEG-2 are input and motion information contained in the encoded data is used or a mode in which moving picture data that do not contain motion information are input, motion information is detected from the moving picture data, and the detected motion information is used, and that perform a picture process according to the motion information.